This invention relates to microwave load pull testing of transistors and other active devices using impedance tuners.
Modern design of high power microwave amplifiers and oscillators, used in various communication systems, requires accurate knowledge of the active device's (microwave transistor, DUT) characteristics. In such circuits, it is insufficient for the transistors, which operate in their highly non-linear regime, close to power saturation, to be described using non-linear numeric models.
A popular method for testing and characterizing such microwave components (transistors) in the non-linear region of operation is “load pull”. Load pull is a measurement technique which allows changing the impedance seen by the DUT in a controlled manner, in order to explore the DUT's performance under such impedance conditions and find the optimum environment conditions for certain performance goals. One widespread technique employs passive microwave impedance tuners and other microwave test equipment for this task; said microwave tuners are used in order to reflect part of the outgoing power from the DUT and thus manipulate the microwave impedance conditions under which the Device Under Test (DUT, or transistor) is tested (FIG. 1).